The invention relates to a DC-DC converter and to a method for controlling a DC-DC converter, in particular for the voltage supply of an on-board electrical system of a hybrid or electric vehicle from a high-voltage network.
In hybrid and electric vehicles, the supply of a low-voltage on-board electrical system can be ensured by the high-voltage network which is used to supply the electrical drive of the hybrid vehicle. To this end, a DC-DC converter, in particular a push-pull converter with a center tap on the secondary side, which extracts energy from the high-voltage network and converts the high voltage of the high-voltage network into a corresponding on-board electrical system voltage.
The DC-DC converter must cover a broad input and output voltage range due to the high voltage fluctuations in the high-voltage network and in the on-board electrical system. In order to counteract this tendency, a step-up converter can, for example, be connected upstream of the DC-DC converter on the high-voltage network side. Alternatively, a multi-stage system comprising a series circuit consisting of DC-DC converters can be used the publications Chen, W.; Ruan, X; Yan, H.; Tse C. K.: “DC/DC Conversion Systems Consisting of Multiple Converter Modules: Stability, Control and Experimental Verification”, IEEE Transactions on Power Electronics, Vol. 24, No. 6, June 2009 and Siri, K; Willhoff, M; Truong, C.; Conner, K. A.: “Uniform Voltage Distribution Control for Series-Input Parallel-Output, Connected Converters”, IEEEAC paper '1074, v. 6, January 2006 each disclose, for example, multi-stage voltage converter structures, which are connected in series on the input side and connected in parallel on the output side. Said multi-stage voltage converters thereby consist of a plurality of voltage converter stages, by means of which the input voltage can be regulated.
There is, however, the need for solutions for the DC-DC conversion in which the DC voltage converters used can be operated at an optimal working point.